ὥστε (ὡς) may be used with a past tense of the indicative with ἄν (potential indicative and unreal indicative).

τοιοῦτόν τι ἐποίησεν ὡς πᾶς ἂν ἔγνω ὅτι ἀσμένη ἤκουσεshe made a movement so that every one could recognize that she heard the music with pleasureX.S. 9. 3, κατεφαίνετο πάντα αὐτόθεν ὥστε οὐκ ἂν ἔλαθεν αὐτὸν ὁρμώμενος ὁ Κλέων τῷ στρατῷeverything was clearly visible from it, so that Cleon could not have escaped his notice in setting out with his forceT. 5.6.